Print hammer assembly for high speed printers



Aug. 16, 1966 H. c. RUSSO 3,266,418

PRINT HAMMER ASSEMBLY FOR HIGH SPEED PRINTERS Filed Dec. 2, 1965 t 39 WiINVENTOR. HUMBERT C. RUSSO aw M/QW ATTORNEYS United States Patent3,266,418 PRINT HAMMER ASSEMBLY FOR HIGH SPEED PRINTERS Humbert C.Russo, Allston, Mass., assig-nor to Anelex Corporation, Boston, Mass., acorporation of New Hampshire Filed Dec. 2, 1963, Ser. No. 327,201 3Claims. (Cl. 101-93) This invention relates to an improved print hammerassembly for a high speed printer, and more particularly to improvementsin print hammer assemblies of the type disclosed and claimed in US.Patent No. 2,940,385 to Frank R. House, entitled High Speed Printer,issued June 14, 1960, and assigned to the assignee of the presentapplication. It is the principal object of the present invention toprovide an improved print hammer assembly having an increased usefullife, for use in high speed printing equipment in which it is requiredto form print images on a moving strip of paper by impressing the paper,with an extremely brief impact, upon selected type characters on thesurface of a continuously-revolving print wheel.

According to the aforementioned patent, very highspeed printing iscarried out by rotatively driving a multiple-column print wheel, in eachcolumn of which is engraved a set of characters, such as an alphabet and.the cardinal numbers, and striking the paper against selectedcharacters as they pass a printing station. A synchronizing generator isdrivingly connected with the print wheel and emits a stream of pulsescorresponding to the arrival of each character in printing position,which pulses are used to produce energization of any of a plurality ofmagnetically-operated hammers to imprint an inked ribbon and paperagainst selected characters in any column of the print wheel. The printwheel is caused to rotate at high speed, and the movements of the printhammers between a rest position and a printing position must necessarilybe extremely rapid, on the order of a few microseconds. If the hammertarries in the printing position for any appreciable time interval, asmeared character will be produced. Further, it is vital that upon thecompletion of the return stroke to rest position, its momentum 'beabsorbed so that it will not rebound to strike the paper a second time;otherwise a ghost impression may be produced, spaced slightly from theoriginal impression. Further, it is necessary that the mechanism exhibitan extremely long useful life in terms of the number of cycles ofoperation :which can be attained.

The aforementioned patent to House provides a hammer bar suspensionincorporating a flexible reed which pivotally mounts the hammer bar in aframe, a separate leaf spring which is secured in the frame andslidingly engages the bar to bias it toward rest position, andclosely-fitting recesses formed in the frame for guiding the bars intheir pivotal movements, thus to prevent sideways motion from thedesired paths. It has been found in practice that this system operatesquite satisfactorily and affords a very considerable period of usefullife. However, a limiting factor in the life span is the frictionalsliding which takes place between the return spring and the hammer bar.

As previously stated, it is the primary object of my invention tofurther increase the useful life of a hammer assembly, and it is arelated object to provide a frictionless hammer suspension whereby thelimiting factor of return-spring friction is obviated. It is a furtherobject to provide a simplified hammer assembly requiring fewer elements,which nevertheless provides a materially increased life in terms ofcycles of useful operation. It is a further object to provide a hammerassembly with improved means for damping the rebound of a print3,266,418 Patented August 16, 1966 hammer from the rest position on itsrapid return from a printing position. Further objects and advantages ofthe invention will become apparent as the following descriptionproceeds.

Briefly stated, according to a preferred embodiment of the' invention, Imount the hammer bar pivotally in the frame means, solely by means of aleaf spring which is accomplished by securing it on complementarymounting surfaces on the frame and bar which are inclined with respectto one another so as to flex the leaf spring about the pivotal axis ofthe bar even in its rest position. Movement of the hammer "bar towardthe printing position further flexes the leaf spring in a direction toincrease the return bias. In consequence, rebounding movement is opposedby a positive bias even in the rest position. However, an electromagnetprovided to drive the bar to printing position must overcome this bias,and the bias is therefore held at a minimum compatible with effectiveprevention of rebound.

According to a further feature, a resilient stop is provided forabsorption of the momentum of the returning hammer and has adjustablepositioning means. The rest position of the hammer is determinative ofits flight time toward the printing position, which must be equal forall the hammer assemblies of a multiple-column printer; to attain thisend, I mount the resilient stop upon a flexible leaf which ispre-stressed away from the printing position, and position the leaf bymeans of a rod threadedly supported in the frame, so that any back-lashmovement is prevented. The position of the resilient rest stop canthereby be precisely fixed to permit accurate control of the hammerfiight time.

While the specification concludes with claims particularly pointing outthe subject matter which I regard as my invention, it is believed that aclear understanding may be gained by the following detailed descriptionof a preferred embodiment thereof, referring to the accompanyingdrawing, in which:

FIG. 1 is a plan view of a hammer module incorporating a plurality ofhammer assemblies;

FIG. 2 is a view in elevation and partially in section, showing a printhammer in a rest position; and

FIG. 3 is a fragmentary sectional view in elevation, showing the printhammer in printing position.

Referring to the drawings, the module includes a series of print hammers10 having impact faces 12 for impressing a moving web of paper 14against type faces (not shown) arranged in corresponding columns on thesurface of a print roll 16, substantially as shown and described in theaforementioned House patent. The individual hammers of the module arespaced apart to admit hammers of a corresponding but opposed modulebetween them, so that each of a closely-spaced series of rows of typecharacters may have operative relation with a corresponding hammer. Asdescribed in the abovementioned House patent, the hammers in the opposedmodule are interspersed with the spaced-apart hammers 10.

Each hammer 10 is formed in one end of an elongated hammer bar 18, andis provided at its opposite end with a ferromagnetic portion 20, whichmay be separately formed and secured to the bar as by brazing. .The bar18 proper and the hammer portion 10 are preferably formed of steel. Thehammers are mounted in a frame generally designated at 22, which is anassembly of a base 3 24, a slotted block 26, and a stop support block28, secured by machine screws 30 and 32.

For energizing the hammers, the ferromagnetic portions 20 extend acrosspole pieces 34 of coils 36, which are connected for selectiveenergization by control means which may be as described in theaforementioned House patent, and of which no further description istherefore believed necessary. Alternate ones of the hammer bars havetheir ferromagnetic portions 20 in right-angular relation to the barsproper, in order to provide suflicient space in the limited width of themodule frame to accomodate the coils 36 associated with each of thecloselyspaced hammers. These bars contain extending portions 21 whichare used as spring mounts as described below. The pole pieces 34 aremounted in suitable recesses 38 formed in the frame, by means ofthreaded fasteners 40. A thin film 42 of resilient material ispreferably placed over the surface of each bar confronting the face of apole piece 34, to avoid direct contact and to reduce wear deriving fromthe impact of the bars. Energization of the coils 36 produces a pivotalmovement of the print ham mer to printing position, as shown in FIG. 3.

The improved hammer assembly includes a series of leaf springs 44, onebeing associated with each hammer, and separated from one another in theassembly by gaps 48. The leaf springs are secured to the slotted block26 by means of a plate 52 and screws 54, in overlying engagement with ashim 50. The plate 52 causes all springs 44 to be rigidly secured to theblock 26 as mounting screws 54 are tightened. Each spring is secured atits free end upon an inclined surface 56 formed on the portion 20 or 21of a corresponding hammer by means of a plate 58 and screw 60. It shouldbe noted that in the rest position shown in FIG. 2, the surfaces 56 areinclined to the common base portion 46 of the leaf springs at an angleA; thereby flexing the individual leaves about an unsupported pivotportion P, which extends across a gap between the block 26 and theportions 20 or 21 of the bars. The unsupported portions include anddefine pivotal axes of the bars, extending transversely to the module.In consequence of the flexure of the leaf springs, they are pre-stressedin the rest position to bias the bars counter-clockwise as viewed inFIG. 2, toward the rest position. Energization of the electromagnets 34,36 to drive the hammers to the print position shown in FIG. 3, increasesthe angle of inclination to a value B indicated in FIG. 3, therebyincreasing the return bias. The leaf springs 44 act as the sole guides,pivotal supports, and return springs for the hammers. The block 26 isformed with slots 62 receiving the bars 18, but these affordconsiderable clearance, as they do not serve to guide the bars, thisbeing the function solely of the leaf springs.

The movements of the hammer bars are limited by stop means comprisingstop screws 64, for determining the printing position, and resilientmembers 66 for determining the rest position. The stop screws 64 arethreaded in common in a nylon nut 68 mounted in the stop block 28, foradjustment to a printing position, which must be substantially uniformfor all hammers. To minimize the period of engagement of the hammerfaces 12 with the paper 14, the parts are so positioned relative to oneanother that the hammer does not engage the stop screws 64 when theferromagnetic portion 20 first engages the pole pieces 34, but themomentum of the hammer is relied upon to produce a Whipping motion ofthe bar 18, carrying the hammer the remaining distance to the stopscrews. A very rapid initial return is thereby ensured.

The spacing of the resilient members 66 from the stop screws 64 iscritical, as it determines the flight time of the individual hammers,which must be substantially uniform to secure good printing quality. Atthe same time, it is desired that the rest stops be resilient to preventrebound by absorbing the momentum of the hammer upon its return to restposition. I achieve precise adjustable positioning of the resilientmembers by mounting them upon leaf supports 70, which are cantileveredbet-ween the base 24 and the slotted block 26, and whose free ends arebent downwardly to bias the stops away from the printing position; andby positioning these spring-supported stops by means of set screws 72which are received in bores 76 formed in the base. The set screws 72 arethreadedly engaged in common in a nylon nut 78 received in the base, toeliminate any looseness or play. In normal adjusted positions, theleaves 70 are flexed upwardly by the screws 72, and their resultingdownward bias holds the members 66 firmly in position. Rebound of theprint hammers is thus effectively damped, and their flight time isaccurately controllable.

It has been found in practice that the improved print hammer assemblyoperates effectively over an extremely long life span, running tohundreds of millions of cycles. This longevity is at least partiallyattributable to the frictionless pivotal suspension and sole support andguidance of the hammer bars afforded by the leaf spring mounting of thehammer bars, and also to the improved resilient rest stop means.

While I have illustrated and described preferred embodiments of myinvention by way of illustration, it will be understood by those skilledin the art that various changes and modifications may be made withoutdeparting from the true spirit and scope of the invention, which Itherefore intend to define in the appended claims without limitation tothe details of the illustrated embodiment.

I claim:

.1. A print hammer assembly for a high speed printer comprising a barhaving a print hammer at one end thereof and a portion of magneticmaterial at the opposite end thereof, said bar being including meansforming a spring-mounting surface that is substantially parallel to theaxis of that portion of said bar that is adjacent said print hammer,frame means formed with a spring-mounting surface, an electromagnetmounted in said frame means, said electromagnet having pole piecesadjacent said magnetic portion and being adapted when energized to pullsaid magnetic portion toward said pole pieces, a leaf spring havingopposite ends secure-d to said springmounting surfaces of said bar andsaid frame means for connecting said frame means to said barintermediate the ends of said bar for pivotal movement thereof and forbiasing said bar toward a rest position, said frame means having opposedrest stop means and printing stop means coacting with said bar to limitsaid bar to pivotal movement between a rest position and said printingposition, said electromagnet being constructed and arranged whenenergized to pivot said bar to said printing position, said rest stopbeing positioned to incline said spring-mounting surfaces with respectto one another in the rest position of said bar thereby to flex saidleaf spring about said pivotal axis into a pre-stressed condition,biasing said bar against said rest stop means in said rest position toprevent rebound of said bar therefrom upon a return of said bar fromsaid printing position.

2. A print hammer assembly for a high speed printer comprising a barhaving a print hammer at one end thereof and a portion of magneticmaterial at the opposite end thereof, said bar being formed with aspringrnounting surface that is substantially parallel to the axis ofthat portion of said bar that is adjacent said print hammer, frame meansincluding means forming a springmounting surface, an electromagnetmounted in said frame means, said electromagnet having pole piecesadjacent said magnetic portion and being adapted when energized to pullsaid magnetic portion toward said pole pieces, a leaf spring havingopposite ends secured to said spring-mounting surfaces of said bar andsaid frame means for connecting said frame means to said barintermediate the ends of said bar for pivotal movement thereof and forbiasing said bar toward a rest position, said frame means having a reststop means coacting with said bar to limit its pivotal movement at saidrest position, said eleotromagnet being constructed and arranged whenenergized to pivot said bar to a printing position, said rest stop beingpositioned to stress said leaf spring when the bar is biased at the restposition, thus permitting said spring to bias said bar against said reststop means in said rest position.

3. A print hammer assembly as recited in olairn 2, together with meansfor ad-justably supporting said resilient member to regulate the strokeof said bar, said supporting means comprising a stop adjustably mountedin said frame, and a leaf spring carrying said resilient member,

cantilivered in said frame, and engaged between said resilient memberand said stop.

References Cited by the Examiner UNITED STATES PATENTS 2,940,685 6/ 1960House 101-93 3, 1 10, 250 11/ 1963 Fradkin 101-93 3,126,823 3 1964Benson l01-93 3,144,821 8/ 1964 Drej za 10l-93 10 3,-177,-8 03 4/ 19 65Antonuoci 101--93 WILLIAM B. PENN, Primary Examiner.

1. A PRINT HAMMER ASSEMBLY FOR A HIGH SPEED PRINTER COMPRISING A BAR HAVING A PRINT HAMMER AT ONE END THEREOF AND A PORTION OF MAGNETIC MATERIAL AT THE OPPOSITE END THEREOF, SAID BAR BEING INCLUDING MEANS FORMING A SPRING-MOUNTING SURFACE THAT IS SUBTANTIALLY PARALLEL TO THE AXIS OF THAT PORTION SAID BAR THAT IS ADJACENT SAID PRINT HAMMER, FRAME MEANS FORMED WITH A SPRING-MOUNTING SURFACE, AN ELECTROMAGNET MOUNTED IN SAID FRAME MEANS, SAID ELECTROMAGNET HAVING POLE PIECES ADJACENT SAID MAGNETIC PORTION AND BEING ADAPTED WHEN ENERGIZED TO PULL SAID MAGNETIC PORTION TOWARD SAID POLE PIECES, A LEAF SPRING HAVING OPPOSITE ENDS SECURED TO SAID SPRINGMOUNTING SURFACES OF SAID BAR AND SAID FRAME MEANS FOR CONNECTING SAID FRAME MEANS TO SAID BAR INTERMEDIATE THE ENDS OF SAID BAR FOR PIVOTAL MOVEMENT THEREOF AND FOR BIASING SAID BAR TOWARD A REST POSITION, SAID FRAME MEANS HAVING OPPOSED REST STOP MEANS AND PRINTING STOP MEANS COACTING WITH SAID BAR TO LIMIT SAID BAR TO PIVOTAL MOVEMENT BETWEEN A REST POSITION AND SAID PRINTING POSITION, SAID ELECTROMAGNET BEING CONSTRUCTED AND ARRANGED WHEN ENERGIZED TO PIVOT SAID BAR TO SAID PRINTING POSITION, SAID REST STOP BEING POSITIONED TO INCLINE SAID SPRING-MOUNTING SURFCACES WITH RESPECT TO ONE ANOTHER IN THE REST POSITION OF SAID BAR THEREBY TO FLEX SAID LEAF SPRING ABOUT SAID PIVOTAL AXIS INTO PRES-STRESSED CONDITION, BIASING SAID BAR AGAINST SAID REST STOP MEANS IN SAID REST POSITION TO PRE VENT REBOUND OF SAID BAR THEREFROM UPON A RETURN OF SAID BAR FROM SAID PRINTING POSITION. 